Separation Techniques

Question 1

What are some methods to collect gases?

Answer 1

1. Using a gas syringe
2. Displacement through water
3. Upward delivery
4. Downward delivery

Question 2

Is hydrogen soluble in water?

Answer 2

No

Question 3

Is carbon dioxide soluble in water?

Answer 3

Slightly/No

Question 4

Is oxygen soluble in water?

Answer 4

Very slightly/No

Question 5

Is chlorine soluble in water?

Answer 5

Yes

Question 6

Is hydrogen chloride soluble in water?

Answer 6

Very soluble

Question 7

Is sulfur dioxide soluble in water?

Answer 7

Very soluble

Question 8

Is ammonia soluble in water?

Answer 8

Extremely soluble

Question 9

What are the drying agents available?

Answer 9

1. Concentrated sulfuric acid
2. Calcium oxide (quicklime)
3. Fused calcium chloride

Question 10

When should concentrated sulfuric acid be used as a drying agent?

Answer 10

Used for most acidic/neutral gases

Not suitable for alkali gases as it would react

Question 11

When should calcium oxide be used as a drying agent?

Answer 11

Used to dry alkali gases

Not suitable for acidic gases that would react with it

Question 12

When should fused calcium chloride be used as a drying agent?

Answer 12

Used to dry gases that cannot react with it such as CO2, oxygen, nitrogen, hydrogen chloride

Cannot be used with ammonia as it would react

Question 13

What is the nature of carbon dioxide gas?

Acid/alkali/neutral

Answer 13

Acidic

Question 14

What is the nature of hydrogen chlorine gas?

Acid/alkali/neutral

Answer 14

Acidic

Question 15

What is the nature of chlorine gas?

Acid/alkali/neutral

Answer 15

Neutral

Question 16

What is the nature of sulfur dioxide gas?

Acid/alkali/neutral

Answer 16

Acidic

Question 17

What is the nature of ammonia gas?

Acid/alkali/neutral

Answer 17

Alkaline

Question 18

How do you determine the purity of a substance?

Answer 18

1. Check its boiling and melting points (should be fixed)
2. Using chromatography

Question 19

What is the effect of impurity on melting and boiling points

Answer 19

1. Cause them to take place over a range of temperatures
2. Decrease melting point, increase boiling point

Question 20

What is the effect of pressure on boiling point?

Answer 20

As pressure increases, boiling point increases

Question 21

What methods can you use to separate solid-solid mixtures?

Answer 21

1. Magnetic attraction
2. Sieving
3. Sublimation
4. Using suitable solvents

Question 22

What methods can you use to separate insoluble solid-liquid mixtures?

Answer 22

1. Filtration

Question 23

What methods can you use to separate soluble solid-liquid mixtures?

Answer 23

1. Evaporation to dryness
2. Crystallisation
3. Simple distillation

Question 24

What methods can you use to separate liquid-liquid mixtures?

Answer 24

1. Separating funnel
2. Chromatography
3. Fractional distillation

Question 25

What is the procedure to carry out crystallisation?

Answer 25

1. Solution is gently heated until saturation in an evaporating dish 2. Cool the solution until crystals are formed 3. After crystals are formed, filter and wash with small amounts of cold distilled water 4. To obtain a dry pure crystal sample, dry between sheets of filter paper

Question 26

What is the purpose of the boiling chips in a simple distillation set up?

Answer 26

To provide sites for formation of small bubbles (reducing bumping cause by big bubbles) or prevents flash boiling when dust particles agitate superheated liquids causing splatter

Question 27

How to perform paper chromatography?

Answer 27

1. Place solvent in container 2. Draw a starting line about 1.5 cm away from the edge of paper with a pencil 3. Apply a small spot of the chemicals to be analysed on the paper. Repeat application to concentrate the spot 4. Carefully lower the paper into the solvent. Ensure the level of solvent is below the starting line 5. When the solvent front nearly reaches the top of the chromatogram, remove the paper from the container and draw the solvent line with a pencil

Question 28

How to calculate Rf (retention factor) value?

Answer 28

Rf value= X/Y X= distance of spot from starting line Y= distance from solvent front to starting line